FIELD OF THE INVENTION
The invention relates to a planar filter for plug connectors, having a plurality of connectible signal lines disposed in rows and columns, a substrate having an opening for each of the signal lines and having a capacitor in the vicinity of the opening for each of the signal lines, each capacitor having a first coating connected to an associated signal line, a second coating connected to ground through a conducting housing, and a layer-like dielectric between the first and second coatings. The invention also relates to a plug connector being intended especially for mounting on printed wiring boards and using the planar filter.
Such multipole plug connectors are used for transmitting digital or analog measurement signals from multiple measuring instruments or for high-speed transmission of information, in order to filter out interference signals. Such a filtering out of interference signals is generally done with capacitors, one of which is provided for each line carrying a signal. To that end, the capacitors are advantageously combined into planar filters and inserted into the plug connectors, and the planar filters are penetrated by the signal lines. For each of the signal lines, at least one capacitor is provided, and the capacitors are disposed on a generally ceramic and in particular aluminum oxide substrate. If the individual signal lines are constructed as pins (press-fit connection) pressed into plastic parts, then there is no way to solder those pins to the coatings of the signal electrodes which extend into the leadthrough. Plug connectors of that kind are described, for instance, in U.S. Pat. No. 3,447,104, U.S. Pat. No. 4,741,710, or Published European Application No. 0 398 807 A2, corresponding to U.S. Pat. No. 4,950,185. In order to make a filter plug connector, planar filters and seals are inserted into the connector housing. The various capacitors of the planar filter are connected to the connector housing for producing the ground connection through grounding springs that engage the outer edge of the planar filter, and are connected to the connection pins inserted into the leadthrough openings through spring clamps for the contact prongs, in order to produce the signal line branches. Moreover, it is difficult to accommodate the capacitors, which are required for effective filtering, on the substrate of the planar filter, since in the known configurations each filter capacitor surrounds the associated signal line. Additionally, there is an annular surface in the immediate vicinity of the signal line. In that surface the ground coating, which is not extended all the way up to the signal line because of the necessary insulation, is missing, and therefore the surface cannot contribute to the capacitance. The goal of that construction is to achieve adequate filtering with closely spaced signal lines, with the filtering also being damped by mechanical jarring. In those configurations it is disadvantageous that from the very outset they have to be mounted with the plug connectors, so that the connection of the signal line to the associated capacitor coating is soldered. However, that kind of soldered connection is not possible if the signal line is constructed as pins that are press-fitted into a plastic plate.